Apparatus for dewatering suspensions and dry-pressing of the dry substance contained therein



KARLERIC LARSSON E'IAL Nov. 19, 1963 3,111,082

APPARATUS FOR DEWATERING SUSPENSIONS AND DRY-PRESSING OF THE DRY REIN 1962 SUBSTANCE CONTAINED THE 3 Sheets-Sheet 1 Filed March 28,

Nov. 19, 1963 Filed March 28 KARL- APPARATUS FOR DEWA OF THE ERIC LARSSON E TAL TERING SUSPENSIONS AND DRY-PRESSING DRY SUBSTANCE CONTAINED THEREIN s Sheets-Sheet 2 Fig.2

V3F15,.5 I I s 5,5 '4

ls l4 13 INVENTOR.

Nov- 19, 1963 KARL-ERIC LARSSON ET AL 3,111,082 APPARATUS FOR DEWATERING SUSPENSIONS AND DRY-PRESSING OF THE DRY SUBSTANCE CONTAINED THEREIN Filed March 28, 1962 3 Sheets-Sheet 3 INVENTOR.

United States Patent 3,111,082 APPARATUS FGR DEWATERING SUSPENSIQNS AND DRY-PRESSING OF THE DRY SUBSTANCE CONTAINED THEREIN Karl-Eric Larsson, Saille, and Oscar Sigurd .lohanssou,

Grunts, Sweden, assignors to Leje 8: Thurne Alrtieholag, Stockholm, Sweden, a corporation of Sweden Filed Mar. 28, 1962, Ser. No. 183,219 Claims priority, application Sweden Jan. 19, 1962 8 Claims. (Cl. 100-447) The present invention relates to means for dewatering suspensions, such as fiber suspensions, wherein the liquid content is separated by straining the suspension under pressure and concentrating the suspended dry substance to a pulp of the desired degree of dryness. It is known to bring about such dewatering and concentration of the suspension by means of a substantially tubular strainer, through which the suspension is caused to flow against the action of a flow resistance provided at the outlet end of the strainer, the partly dewatered pulp being continuously compressed in a part of the strainer tapering toward the outlet under the influence of the operating pressure prevailing in the strainer, which pressure may be created in known manner by a feed gear provided Within the strainer. The present invention particularly relates to apparatus of the latter kind and has for its object to increase the dewatering capacity of such apparatus, so that the product leaving the strainer attains a degree of dryness as high as possible. According to the invention, this is brought about by having the partly dewatered pulp, on having been compressed and dewaterecl further in the tapering part of the strainer, compressed to the consistency of a compact plug of pulp in a portion of the strainer located near the outlet thereof, in which the pulp is subjected to the influence of a pressure acting substantially only in the axial direction, and from which the pulp flows out against a varying, preferably yielding counterpressure. By controlling this counterpressure, while maintaining the requisite operating pressure, the moisture of the final product may be reduced to an extent not previously reached in dewatering apparatus of the kind under conside-ration.

The invention will be described more closely with reference to the accompanying drawings. FIG. 1 is a longitudinal section through a screw press constructed in accordance with the invention. FIG. 2 is a longitudinal section through the end section of the strainer mantle of the screw press. FIG. 3 shows the feed gear provided with a helicoidal member separate from the t tread of the screw. FIG. 4 shows the latter construction in perspective.

The screw press consists of a tubular strainer 1 and feed gear 2 a ranged therein. The strainer has a cylindrical mantle and an end portion connected thereto, the end portion comprising three conical mantle sections 3, 4 and 5. The mantles are provided with flanges 6, 7, by which the cylindrical and conical mantle portichi s are united with one another. Provided at the inlet end of the feed gear is an inlet drum 8, which is connected to the cylindrical mantle and to a plate 9 closing said mantle, which plate is in turn secured to a pedestal it). This pedestal forms one head wall of the machine frame carrying the screw press, the other head wall 11 of the machine frame being rigidly connected with an annular flange 12 ice extending from the mantle section 5. The support ll), 11 is arranged on a base plate 14 together with a bearing frame 13.

The shaft 15 of the feed gear is mounted at one end in the bearing stand 13 and at the other end in a bearing 16. The conical mantle portion 3 converges toward the outlet end of the screw press, while the mantle portion 4 has a taper diverging toward the outlet end and the mantle portion 5 has a taper converging toward the outlet end. The cylindrical part of the mantle is perforated as are also the conical mantle portions 3, 4 so as to let through the water escaping in the pressing operation. On the other hand, the mantle portion 5 connected to the outlet 17 is not perforated. The thread of the feed gear is adapted to the various diameters of the mantle portions so as to merge with a small play in the inner mantle surfaces. The outermost end of the screw thread operates within the conical mantle portion 4, and consequently no part of the thread is caused to operate within the space defined by the conical mantle portion 5.

The material fed in through the inlet drum 8 and consisting of a suspension of solid particles, such as a wood fiber suspension or a suspension containing outlet sludge, is conveyed by the feed gear toward the outlet of the strainer for continuous compression and dewatering. The dewatering substantially takes place in the cylindrical portion of the strainer and Within the first conical mantle section 3, where the pulp is compressed radially. The dry substance thus dewatered and compressed to a compact pulp is forced out through the outlet against the action of a pressure created by a valve 18 cooperating with the outlet end 5 of the mantle, said valve being pressed at a suitably adapted pressure against the escaping dry pulp. In the example shown, the pressing pressure is created pneumatically by means of an annular plunger 19, which is movable in an annular space 21 within a cylinder it which may be actuated by means of compressed air supplied through a conduit 22. The cylinder 20 is rigidly arranged in the machine frame, in a manner such that the annular cylinder space 2; surrounds the shaft $5 of the feed gear. The valve 18 is connected with the plunger 19 by means of a cylindrical member 23. The edge of the flange l2 surrounding the outlet opening forms a valve seat for the valve body 18 in the closed position thereof. During the straining operation the valve body 18 brings about a restriction of the outlet to such an extent that a counterpressure required for the straining and the compression or" the pulp is obtained. The water pressed out escapes to a trough 24 arranged between the frame members ll), 11, said trough being connected to an outlet 25. Provided on the inside of the cylindrical part of the strainer mantle are a number, e.g., four, of longitudinally extending bars 26 or the like intended to prevent the pulp from being rotated by the action of the feed gea Such bars are not required in the straining of ordinary fibrous pulp but are necessitated only in those cases where the pulp contains a large quantity of sludge. The pulp pressed out through the outlet opening 17 falls down onto a band conveyor 27 arranged between the frame members 11, 13, by means of which conveyer the material is carried off in the transverse direction of the screw press. he feed gear is driven at a suitable gear ratio from a motor which is not shown in the drawing, which motor is connected to the end 23 of the feed gear.

. 3 Provided over the strainer is a protective hood 29, the space between the hood and the strainer communicating with the trough 24.

The screw press operates in the following manner:

Prior to starting, the outlet is closed by the valve 18. The suspension fed to the press is, under the influence of the rotating feed gear, subjected to an axial pressure, which brings about dewatering and a successively increasmg concentration of the suspension. The substantial dewatering takes place in the cylindrical portion of the strainer. When passing through the conical section 3 the pulp is also compressed in a radial direction inwardly, the pulp being then dewatered further to an extent to form a compact plug of pulp when passing through the sections 4, 5, said plug being, under the influence of the axial pressure created by the feed gear, pressed out through the outlot 17 while overcoming the exit resistance created by the valve 18. After the pulp has passed the conical section 3, the dewatering process is substantially completed, the pulp then having a water content of approximately 75%. By controlling the pressure on the valve body 18 the exit resistance may be regulated so that the pressure required for the dewatering process is maintained. After the pulp has left the conical section 3, the compression may continue through the mantle sections 4 and 5, Without any risk of the outlet becoming clogged by reason of the compression of the pulp. When the pulp penetrates into the outwardly Widening mantle section 4, the fibers of the pulp have an opportunity to expand, the radial pressure diminrshing and the resistance to the movement in the axial direction being reduced. The cells filled with liquid between the solid particles, which have been closed by the pressure in the section 3 will then expand so that they can communicate with each other. During the following compression of the pulp in the section 5, an immaterial quantity of liquid will be pressed out, which may escape rearwardly through the portions of the pulp compressed to a lesser extent and through the perforations in the section 4. The fixed counterpressure created in the conical section 5 by the compression cooperates with the variable and yielding pressure caused by valve 18 to bring about a suitable axial counterpressure. The taper of mantle section 5 is so adapted, however, that it cannot bring about any clogging of the outlet opening 17, this being also prevented by the fact that said section 5 opens into the outlet and thus makes it possible for the pulp particles to be rearranged while breaking up and disintegrating the pulp plug. The sections 4, 5, in which the pulp is compressed to a compact plug, should be formed in such manner that they do not offer any great resistance to the movement of the pulp toward the outlet. Furthermore, they should be so devised that the pulp upon being dewatered in the section 3 will not be compressed again to such an extent as to prevent the pulp from passing to the outlet through the section 5, where the compression is comparatively small. The threads of the feed gear preferably extend only into the section 4, and at any rate they should not extend into the section 5.

The mantle portions 4 and 5 need not necessarily be conical but may be replaced by "a cylindrical mantle memher having the same internal diameter as that of the end of the conical mantle member 3. The arrangement shown of two conical portions 4 and 5 turned in opposite directlons has the advantage, however, that a portion of the water remaining after the passing of the section 3 may be caused to escape through the section 4, and the further advantage that the pulp may be subjected to a further compressing action prior to the exit and is thus dewatered further in a rearward direction, while the compression in the section 5 forms at the same time a fixed resistance to the exit, which may be adapted to cooperate in a suitable The end portion of the strainer mantle containing the mantle sections 3, 4 and 5 is shown on a larger scale in FIG. 2, which illustrates suitable axial lengths and cone angles for the various sections, which have proved to be particularly suitable for the dewatering of suspensions to a degree of dryness as great as possible. The angles denoted by V V and V which constitute half of the top angle of the respective cones, have in the example shown the values l5.5, 3.5 and 5.5 respectively, the ratio V :V being approximately 5:1, while the ratio V :V is approximately 3:1. These figures indicate the sizes of the angles and their mutual ratios, but small deviations may of course occur in practice. The axial lengths of the sections are designated by l l and respectively. In the example shown l =l but the ratio :1 and 1 :1 respectively may vary between 3 :1 and 2: l. The cylindrical portion of the strainer mantle may have an internal diameter of 2530 cm.

FIGS. 3 and 4 show a modification of the thread of the feed gear. The thread producing the compression terminates in the compression section 3, a portion of a similar thread 30, which only comprises about 180 of the circumference, being arranged outside the end of the firstmentioned thread near the outlet thereof, preferably in the section 4, which thread is adapted to facilitate the feeding-out of knots, bark and other larger pieces occurring in the pulp. Said thread has a generatrix inclined toward the shaft 15, the angle of said generatrix to the shaft equaling approximately the corresponding angle of the conical end of the valve body 18, so that the latter may be introduced in a closed position without being prevented by the thread 30. In FIG. 4 said thread is shown as being out along a generatrix, a corresponding section 3 1 illustrating the inclination of the generatrix to the shaft.

Two screw presses of the construction above described may according to the invention be built together to form a twin unit, the two strainers being coaxially arranged and turned by 180 toward one another with an axis com mon to both of the feed gears. In such a construction it will be found suitable to arrange a feeding-in drum common to both of the strainers half-Way between the strainers, the feed gears 2 feeding the suspension in opposite directions toward outlets located at opposite ends of the units. The bearing 16 may then be common to both of the feed gears. The two strainers may also be arranged coaxially in such manner that the feeding in procedure takes place at opposite ends of the unit, feedingout then taking place through a common outlet arranged between the strainers.

What is claimed is:

1. An apparatus for dewatering solid-liquid suspensions comprising a tubular strainer having an inlet end and an outlet end and having a conical section tapering toward said outlet end, and an outlet section joining the conical section at one end and forming at the other end a discharge outlet, a feed screw disposed coaxially within the strainer, a valve body controlling said discharge outlet, and means for actuating said valve body so as to produce an axially-yielding counter-pressure on the solid material discharged, said outlet section comprising two conical mantle portions tapering in opposite directions toward'the conical section and the discharge outlet respectively, whereby the compressed material passing therethrough is first caused to expand and then to be pressed together.

2. An apparatus as defined in claim 1, wherein the cross-sectional areas of the outlet section at both ends thereof are substantially the same as that of the end of the conical section connected to the outlet section.

3. An apparatus as defined in claim l, wherein the axial lengths of the two conical mantle portions are substantially equal.

4. An apparatus as defined in claim 3, wherein the axial length of the conical section of the strainer is about 2 to 3 times greater than the length of each conical mantle portion of the outlet section.

5. An apparatus as defined in claim 1, wherein the cone angle of the conical section of the strainer is about 5 times greater than the cone angle of the adjacent conical mantle portion of the outlet section.

6. An apparatus as defined in claim 1, wherein the conical mantle portion of the outlet section adjacent said conical section is perforated, whereas the other mantle portion tapers toward the discharge outlet and is imperforate.

7. An apparatus as defined in claim 1, wherein the thread of the feed screw terminates in the mantle portion adjacent said conical section.

8. An apparatus as defined in claim 1, wherein said valve body has a conical surface and wherein a separate References Cited in the file of this patent UNITED STATES PATENTS 1,851,191 Lang Mar. 29, 1932 2,615,387 Messing .d Oct. 28, 1952 2,903,960 Zies Sept. 15, 1959 3,003,412 Vincent Oct. 10, 1961 

1. AN APPARATUS FOR DEWATERING SOLID-LIQUID SUSPENSIONS COMPRISING A TUBULAR STRAINER HAVING AN INLET END AND AN OUTLET END AND HAVING A CONICAL SECTION TAPERING TOWARD SAID OUTLET END, AND AN OUTLET SECTION JOINING THE CONICAL SECTION AT ONE END AND FORMING AT THE OTHER END A DISCHARGE OUTLET, A FEED SCREW DISPOSED COAXIALLY WITHIN THE STRAINER, A VALVE BODY CONTROLLING SAID DISCHARGE OUTLET, AND MEANS FOR ACTUATING SAID VALVE BODY SO AS TO PRODUCE AN AXIALLY-YIELDING COUNTER-PRESSURE ON THE SOLID MATERIAL DISCHARGED, SAID OUTLET SECTION COMPRISING TWO CONICAL MANTLE PORTIONS TAPERING IN OPPOSITE DIRECTIONS TOWARD THE CONICAL SECTION AND THE DISCHARGE OUTLET RESPECTIVELY, WHEREBY THE COMPRESSED MATERIAL PASSING THERETHROUGH IS FIRST CAUSED TO EXPAND AND THEN TO BE PRESSED TOGETHER. 